Apparatus and method for obtaining information related to terahertz waves

ABSTRACT

To provide an apparatus capable obtaining a temporal waveform of terahertz waves transmitted through or reflected by a sample in a set region. A delay unit is configured to change a timing at which the detection unit detects terahertz waves transmitted through or reflected by a sample, which is originated from terahertz waves generated by a generation unit. A waveform obtaining unit is configured to obtain a temporal waveform of the transmitted terahertz waves which are obtained by using the delay unit. The delay unit, of which more than one may be used, is controlled so that the detection unit detects the transmitted terahertz waves in an area related to the temporal waveform set on the basis of information related to the sample that is pre-stored in the storage unit. Then, a temporal waveform of the transmitted terahertz waves in the area is obtained.

RELATED APPLICATIONS

This application is a continuation of patent application Ser. No.12/193,121, filed Aug. 18, 2008, now U.S. Pat. No. 7,551,269, issuedJun. 23, 2009, claims benefit of the filing date of that patent under 35U.S.C. §120, claims benefit of the filing dates of Japanese patentapplications nos. 226338/2007 and 159315/2008, filed Aug. 31, 2007, andJun. 18, 2008, respectively, under 35 U.S.C. §119, and incorporates theentire disclosure of each of the three mentioned priorpatents/applications herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and a method of obtaininginformation related to terahertz waves that are transmitted through orreflected by a sample.

2. Description of the Related Art

A terahertz wave is an electromagnetic wave having an arbitraryfrequency band from 0.03 THz to 30 THz. In a terahertz wave band,characteristic absorptions that depend on structures and states ofvarious substances that include biological molecules occur. Utilizingsuch characteristics, an inspection technology for an analysis and anidentification of a substance in a nondestructive manner has beendeveloped. Also, an application to a safe imaging technology as asubstitute for X-rays or a high-speed communication technology isexpected.

In addition, the characteristics of terahertz waves include a moderateability to penetrate a sample. For example, a technology for measuring afilm thickness of a multilayer film, utilizing this property, isdisclosed (Japanese Patent Laid-Open No. 2004-28618). According toJapanese Patent Laid-Open No. 2004-28618, on the basis of a plurality ofterahertz wave pulse responses, the film thickness of the multilayerfilm is determined. These pulse responses are obtained by sampling atime response waveform of the terahertz wave with a probe light.According to this method, the sampling is carried out over allmeasurement time regions.

In recent years, one application of this property of terahertz waves hasbeen a technology for measuring or inspecting the product quality oftablets in a nondestructive manner. For example, an application to atechnology for measuring or inspecting the coating thicknesses of asugar-coated tablet, a film-coated tablet, and the like is expected.These coating thicknesses affect the disintegration properties orresolvability of the tablets. Also, the tablets are formed by mixing apowdered medicinal agent and an additive. For that reason, anapplication to a technology for measuring or inspecting the uniformityof the contained amount of the medicinal agent with respect to theadditive is hoped for.

These characteristic features directly affect medicinal effects of thetablets. For that reason, a technology for controlling and maintainingthe product quality of the tablets is important. At the moment, for thispurpose, a portion of the manufactured tablets is extracted, and adestructive inspection is carried out.

According to Japanese Patent Laid-Open No. 2004-28618, a method ofshortening a period of time needed to measure the film thickness of themultilayer film is sought.

In addition, in a case where quality control for tablets is performed,instead of the sampling inspection, in future, it may be desired toeffect a constant inspection during the manufacturing process, so thatall the tablets can be inspected. In order to carry out such a processinspection, a method of measuring and inspecting the samples in anondestructive manner is desirable, but a method by which this could beachieved has not yet been established. In particular, for the processinspection for medicinal tablets, from a standpoint that a large numberof samples are dealt with in a short period of time, a method ofmonitoring the state of a single table in a still shorter period of timeis ideal.

SUMMARY OF THE INVENTION

The present invention provides an apparatus capable obtaining a temporalwaveform of terahertz waves which are transmitted through or reflectedby a sample in a set region. Also, the present invention provides anapparatus capable shortening the period of time needed to obtaininformation related to the sample (film thickness or the like) by usingthe temporal waveform in the region as compared with a case of obtainingall regions of the temporal waveform.

In view of the above, the terahertz wave detection apparatus accordingto an aspect of the present invention has the following configuration: adetection unit arranged to detect a terahertz wave from a sample and aninformation storage unit arranged to previously store internalinformation which becomes a standard of the sample. The terahertz wavedetection apparatus also includes a delay optical unit arranged toadjust a timing at which the detection unit is operated by changing adelay time with respect to a pump light of a probe light incident on thedetection unit. The terahertz wave detection apparatus also includes adelay time adjustment unit arranged to set a measurement area desired tobe measured on the basis of the information which becomes the standardin the storage unit and adjust the delay time in the measurement area.The terahertz wave detection apparatus also includes a reconstructionunit arranged to reconstruct the internal information on the sample onthe basis of the output of the detection unit and an adjustment amountof the delay time by the delay time adjustment unit.

The terahertz wave detection method according to an aspect of thepresent invention has the following steps (a) to (e):

(a) previously storing internal information which becomes a standard ofa sample;

(b) adjusting a timing of detecting a terahertz wave in a detection stepby way of a delay time with respect to a pump light of a probe light;

(c) setting a measurement area desired to be measured on the basis ofthe information which becomes the standard in the information storagestep and adjusting a delay time in a delay optical step in themeasurement area;

(d) detecting the terahertz wave from the sample; and

(e) reconstructing the internal information on the sample on the basisof an output in the detection step and an adjustment amount in the delaytime adjustment step.

An inspection system according to an aspect of the present invention hasthe following configuration: a detection unit arranged to detect aterahertz wave from a sample and an information storage unit arranged topreviously store internal information which becomes a standard of thesample. The inspection system also includes a delay optical unitarranged to adjust a delay time of a probe light incident on thedetection unit with respect to a pump light. The inspection system alsoincludes a delay time adjustment unit arranged to set a measurement areadesired to be measured on the basis of the information which becomes thestandard in the storage unit and adjust the delay time of the probelight in the measurement area. The inspection system also includes aprocessing unit arranged to reconstruct the internal information on thesample on the basis of an output of the detection unit and an adjustmentamount of the delay time by the delay time adjustment unit. Theinspection system also includes a comparison unit arranged to comparethe internal information on the sample obtained by the processing unitwith the internal information which becomes the standard of the samplestored in the information storage unit. The inspection system alsoincludes an apparatus control unit arranged to carry out screening ofthe sample or adjust a manufacturing condition of the sample inaccordance with the comparison result of the comparison unit.

An apparatus for obtaining information related to a terahertz wavetransmitted through or reflected by a sample according to another aspectof the present invention includes: a generation unit arranged togenerate a terahertz wave; a detection unit arranged to detect aterahertz wave transmitted through or reflected by a sample which isoriginated from the terahertz wave generated by the generation unit; adelay unit arranged to change a timing for the detection unit to detectthe terahertz wave; a storage unit arranged to previously storeinformation related to the sample; and a waveform obtaining unitarranged to obtain a temporal waveform of the transmitted or reflectedterahertz wave which is obtained by the delay unit, in which the delayunit is controlled to allow the detection unit to detect the terahertzwave in an area related to the temporal waveform set on the basis of theinformation related to the sample previously stored in the storage unit,and a temporal waveform of the transmitted or reflected terahertz wavein the area is obtained.

A method of obtaining information related to a terahertz wavetransmitted through or reflected by a sample according to another aspectof the present invention includes: generating a terahertz wave;detecting a terahertz wave transmitted through or reflected by a samplethe terahertz wave which is originated from the generated terahertzwave; obtaining a temporal waveform of the transmitted or reflectedterahertz wave by changing the detection timing; changing the timing soas to detect the transmitted or reflected terahertz wave in an arearelated to the previously obtained temporal waveform set on the basis ofthe temporal waveform of the terahertz wave transmitted through orreflected by the sample; and obtaining a temporal waveform of thetransmitted or reflected terahertz wave in the area.

According to the various aspects of the present invention, themeasurement reference related to the internal information which servesas the standard of the sample is pre-stored in the information storageunit, and on the basis of the measurement reference, the reaching timeof the terahertz wave reaching the detection unit is predicted.According to the embodiments of the present invention, the delay timeadjustment unit adjusts the delay time through switching in adiscontinuous manner so that the delay time of the probe light foroperating the detection unit corresponds to the reaching time of theterahertz wave. For that reason, it is possible efficiently to detectthe terahertz wave necessary for obtaining the sought internalinformation on the sample (for example, the peak of the pulse of thereflected terahertz waves). On the basis of the output of the detectionunit and the adjustment amount of the delay time adjustment unit, theprocessing unit computes the internal information on the sample. As inthe mode of detecting only the necessary part on the basis of themeasurement reference, it is possible to efficiently obtain internalinformation on the sample.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of an apparatus according toa first embodiment of the present invention.

FIG. 2 is an explanatory diagram for describing an operation forobtaining internal information on a tablet as an example.

FIG. 3 is a schematic configuration diagram of an apparatus according toa second embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of an apparatus according toa third embodiment of the present invention.

FIG. 5 illustrates a mode example of a delay optical unit of theapparatus according to an embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of a part of an apparatusaccording to a sixth embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of a part of the apparatusaccording to the sixth embodiment of the present invention.

FIG. 8 is an explanatory diagram for describing an irradiation modeexample of terahertz waves.

FIG. 9 is a schematic configuration diagram of a part of an apparatusaccording to a fifth embodiment of the present invention.

FIG. 10 is a schematic configuration diagram of a part of the apparatusaccording to the fifth embodiment of the present invention.

FIG. 11 is an explanatory diagram for describing a structure of a fiberlaser.

FIG. 12 is an explanatory diagram for describing an amplification unitof the fiber laser of FIG. 11.

FIG. 13 is an explanatory diagram for describing a dispersioncompensation unit of the fiber laser of FIG. 11.

FIGS. 14A and 14B are explanatory diagrams for describing a structurefor carrying out pulse compression.

FIGS. 15A and 15B are explanatory diagrams for describing an operationof the apparatus according to the first embodiment of the presentinvention.

FIG. 16 illustrates a propagation path example of a transmitted pulsewave according to the second embodiment of the present invention.

FIGS. 17A and 17B are schematic diagrams for describing an apparatusaccording to an embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

An apparatus and a method according to the preferred embodiments of thepresent invention will be described with reference to the drawings. Itis noted that the present invention is not limited to these embodiments,and without departing from the scope of the present invention,modifications are not to be considered excluded from the presentinvention.

(Apparatus for Obtaining Information Related to Terahertz Wave)

An apparatus according to the embodiments of the present invention willbe described with reference to FIGS. 17A and 17B. Herein, FIGS. 17A and17B illustrate an apparatus for obtaining information related toterahertz waves transmitted through a sample. It is noted that thepresent invention is not limited to reflection, but as in this firstembodiment or as illustrated in FIG. 1, an apparatus for obtaininginformation related to transmitted terahertz waves may also be used.

A generation unit 12 is configured to generate terahertz waves. Then, adetection unit 13 is configured to detect terahertz waves 11 transmittedthrough a sample 19, which is originated from terahertz waves 10generated by the generation unit 12. It is noted that details of thegeneration unit 12 and the detection unit 13 in the first embodiment aredescribed below.

A delay unit 14 is configured to change a timing at which the detectionunit 13 performs the detection. As illustrated in FIG. 17A, in order tocontrol the distance over which the generated terahertz waves 10 topropagate, the delay unit 14 can be configured to change the distancebetween the generation unit 12 and the detection unit 13. For example, astage for moving the generation unit 12 is provided, and by changing thedistance between the generation unit 12 and the detection unit 13 whilemoving the stage, it is possible to change the distance over which theterahertz waves 10 propagates.

Herein, as in a delay unit 24 of FIG. 17B, it is also possible tocontrol the propagation speed of the generated terahertz waves 10, thisbeing done by adopting a configuration such that the refractive index ofthe propagating region can be changed. For example, by locating a member(a dielectric or the like) having a tropism closer to the terahertz wavetransmitted through the sample, it is possible to change the refractiveindex of the propagating region.

With these configurations, it is possible to retard the time at whichthe terahertz waves reaches the detection unit 13.

In addition, as will be described later, the delay unit can also beconfigured by changing the timing of generation of the terahertz wavesand the time of detection of the terahertz waves, or both. As an exampleof this configuration, a mirror which moves in an optical axis directionfor optical delay is provided (equivalent to a delay optical unit 104 inFIG. 1). At this time, a laser unit arranged to irradiate the generationunit 12 and the detection unit 13 with laser light (which is denoted byreference numeral 101 in FIG. 1) is used. Also, a beam splitter forsplitting the laser light is used. The laser beams resulting fromsplitting by the beam splitter are respectively irradiated to thegeneration unit 12 and the detection unit 13. The laser beam directed tothe detection unit 13 is transmitted through the delay unit (the mirrormoving in the optical axis direction).

Furthermore, the delay unit can also be configured to effect anelectrical delay. For example, the configuration can be realized byretarding the time of a signal generated for mixing with the detectedterahertz wave signal.

A storage unit 16 is configured to pre-store information related to thesample 19. Herein, the information related to the sample 19 pre-storedby the storage unit 16 is preferably a previously obtained temporalwaveform of terahertz waves transmitted through the sample. Theterahertz waves used to produce this information would preferably havethe same characteristics as does that used in the apparatus of theinvention. Also, the information related to the sample 19 includes, forexample, the size (thickness) of the sample, the refractive index, thetransmittance, the reflectivity, the absorbency index, etc. Furthermore,certain physical properties of the sample 19, such as the crystalstructure, the composition, and the like, such as the water content,which can be derived from the above-described information, may be used.It is noted that the present invention is not limited to theabove-described information, however, and further specific descriptionwill be provided below.

A waveform obtaining unit 15 (equivalent to a processing unit 107 inFIG. 1) is configured to obtain the temporal waveform of the terahertzwaves by using the delay unit 104. Herein, the waveform obtaining unit15 samples the terahertz waves detected by the detection unit 13 on thebasis of the timing changed by the delay units 14 and 24, and it is thuspossible to obtain the temporal waveform of the transmitted terahertzwaves.

The delay units 14 and 24 are controlled so that the detection unit 13detects the terahertz waves in the region related to the temporalwaveform which is set on the basis of the information related to thesample 19 pre-stored in the storage unit 16. The control may be carriedout by the waveform obtaining unit 15. Then, it is possible to obtainthe temporal waveform of the transmitted terahertz waves in the region.With this configuration, it is possible to obtain the informationrelated to the sample 19. Also, by obtaining the temporal waveform inthe area, it is possible to shorten the period of time for obtaining theinformation related to the sample 19 as compared with a procedure inwhich one obtains all regions of the temporal waveform.

Herein, the region related to the temporal waveform may, for example, bethe pulse of the temporal waveform is conceivable (for example, (1),(2), (3), and (4) in FIG. 2). Also, as the region related to thetemporal waveform, the peak of the pulse can instead be used.Furthermore, a part having a large absolute value of the pulse gradientor the like is also usable this purpose.

The pulse is a characteristic area of the temporal waveform of thetransmitted terahertz waves. Therefore, by obtaining the pulse, it ispossible to find information related to the sample. For example, fromthe intervals between the pulses, it is possible to derive the thicknessthe sample 19. It is noted that the “characteristic area” is not limitedto the pulse, and an arbitrary area may be used, chosen from variousportions of the temporal waveform of the transmitted terahertz waves.

(Obtaining Information Related to Sample or State of Sample)

From the temporal waveform of the transmitted terahertz waves in theregion, it is possible to obtain information related to the sample. Theinformation related to the sample is, for example, the size (thickness)of the sample, the refractive index, the transmissivity, thereflectivity, the absorbency index, etc. From the above-describedinformation, it is possible to derive the physical properties of thesample, the crystal structure, the composition, and the like, forexample, the water content.

In addition, the temporal waveform of the transmitted terahertz waves inthe region (or the pulse of the temporal waveform of the transmittedterahertz waves in the region) is preferably compared with theinformation pre-stored in the storage unit (for example, the pulse ofthe previously obtained temporal waveform of the terahertz wavestransmitted through the sample). With this configuration, it is possibleto derive the state of the sample.

Herein, the “state of the sample” being referred to is particularly adifference between the physical properties of the sample, the crystalstructure, the composition, and the like, and the previously obtainedinformation (the pulse of the temporal waveform, or the like).

It is noted that the information related to the sample and the state ofthe sample are not limited to the above-described information and state,as described below.

(Accumulation Processing while Counting Measurement Times)

It is preferable that the number of times to measure the sample iscounted, the measured terahertz waves detected by the detection unit areaccumulated, and the accumulation value and the measurement times areused to obtain an average intensity of the terahertz waves. Thesedetails will be described with reference to a sixth embodiment, below.

(Fiber Laser)

It is preferred to provide a fiber laser for generating a pulse laser.An optical fiber can be used as an oscillation medium of the laser. Inaddition, the generation unit is preferably a photoconductive elementfor generating the terahertz waves by means of operation (lasing) of thepulse laser. Furthermore, the detection unit is preferably aphotoconductive element for detecting the terahertz waves through theirradiation of the pulse laser. For the photoconductive element,low-temperature growth GaAs or InGaAs can be used.

Details of the fiber laser will be described with reference to a seventhembodiment, below.

(Method of Obtaining Information Related to Terahertz Wave)

A method of obtaining information related to the terahertz wavestransmitted through or reflected by the sample according to anotherembodiment of the present invention will now be described.

First, the terahertz waves are generated.

Next, terahertz waves transmitted or reflected by a sample, which areoriginated from the generated terahertz waves, are detected. Herein, thereflected terahertz waves are preferably a pulse reflected by arefractive index boundary face of the sample coated with a coating film.It is noted that a detail of the coating film will be described in thefirst embodiment, FIG. 2, and the like.

Also, by changing the detection timing, the temporal waveform of theterahertz waves is obtained.

In addition, the region related to the temporal waveform is set on thebasis of the previously obtained temporal waveform of the terahertzwaves transmitted through or reflected by the sample. Then, the timingis changed so that the transmitted terahertz waves are detected in thearea. With this configuration, it is possible to obtain the temporalwaveform of the transmitted terahertz waves in this region.

Herein, it is possible to obtain the information related to the samplefrom the temporal waveform of the transmitted terahertz waves in theregion. The information related to the sample is, for example, the size(thickness) of the sample, the refractive index, the transmissivity, thereflectivity, the absorbency index, or the like. From theabove-described information, it is possible to derive the physicalproperties of the sample, the crystal structure, the composition, andthe like, for example, the water content.

In addition, the temporal waveform of the transmitted terahertz waves inthe region (or the pulse of the temporal waveform of the transmittedterahertz waves in the region) is preferably compared with the pulse ofthe previously obtained temporal waveform of the terahertz wavestransmitted through the sample. With this configuration, it is possibleto derive the state of the sample.

Herein, the “state of the sample” being discussed is particularly adifference between the physical properties of the sample, the crystalstructure, the composition, and the like, and the previously obtainedinformation (the pulse of the temporal waveform, or the like). It isnoted that the information related to the sample and the state of thesample are not limited to the above-described information and state, anddetails thereof will be further described in the first embodiment.

According to the embodiments of the present invention, a sample theinternal information of which can be estimated is set as a target. Then,this internal information is set as standard information and regarded asa measurement reference. For example, a reference is made to themeasurement reference based on this standard information, and ameasurement area in a depth direction of the sample (for example, in thevicinity of the refractive index boundary face, an area wherecontamination is easily generated, a material having a desired physicalproperty, or the like) is selected. The measurement is carried out onlyin this selected area, and the standard information regarding themeasurement part is updated, so that the reconstruction is performed.

According to the embodiments of the present invention, on the basis ofthese measurement results and the standard information in the selectedmeasurement area, it is also possible to reconstruct a time responsewaveform. By using this response waveform, a spectrographic analysis ofthe sample or imaging is carried out. Also, by comparing this responsewaveform with the standard information of the sample functioning as thereference, screening of the sample and adjustment of the apparatus arecarried out.

Hereinafter, more specific embodiments will be described with referenceto the drawings.

EMBODIMENTS First Embodiment Reflection Type

The present embodiment represents a configuration example of theterahertz wave detection apparatus according to the present invention.FIG. 1 illustrates a configuration example of the terahertz wavedetection apparatus according to the present invention. As illustratedin FIG. 1, the terahertz wave detection apparatus according to thepresent embodiment is composed of a laser unit 101, a generation unit102, a detection unit 103, the delay optical unit 104, a delay timeadjustment unit 105, an information storage unit 106, and the processingunit 107. Also, FIG. 1 illustrates a mode in which a sample 109 isconveyed by a conveyance unit 108. It is noted that the sample 109 doesnot necessarily have to be conveyed for application of the invention.

The laser unit 101 is a part for driving the generation unit 102 and thedetection unit 103 by means of laser light. Hereinafter, laser light fordriving the generation unit 102 may be referred to as “pump light”, andlaser light for driving the detection unit 103 may be referred to as the“probe light” in some cases. According to the present embodiment, thelaser unit 101 uses a titanium-sapphire laser having a pulse width-of 50fsec, a center wavelength of 800 nm, and a cyclic frequency of 76 MHz.

The generation unit 102 is a part for generating the terahertz wavesthrough the pump light incoming from the laser unit 101. According tothe present embodiment, as the generation unit 102, a photoconductiveelement having an antenna pattern formed on a semiconductor thin film isused. To be specific, as the semiconductor thin film, low-temperaturegrowth GaAs (LT-GaAs) formed through molecular-beam low-temperatureepitaxial growth (250° C.) is used for a semi-insulating galliumarsenide (SI-GaAs) substrate (specific resistance >1×10⁷ Ω·cm). Then, adipole antenna made of gold (Au) (the antenna length of 30 μm, theconductor width of 10 μm) having a gap of 5 μm at the center is formedon LT-GaAs. To generate the terahertz waves, in a state where this gapis applied with a bias of 10 V, the pump light is irradiated. As aresult, pulsed terahertz waves having a half-bandwidth of about 200 fsecare generated. It is noted that the antenna shape is not limited to theshape just described. For example, a bow-tie antenna or a spiralantenna, which is a common wideband antenna, may also be used. Also, thesemiconductor thin film is not limited to the above configuration, and,for example, a semiconductor material such as indium gallium arsenide(InGaAs) may also be used. Also, the semiconductor material itself mayalso be used for the generation unit 102. For example, a mirror polishedGaAs surface is irradiated with the pump light, and the terahertz wavesare generated through the time change of a momentary current generatedat this time. Also, an organic crystal such as DAST(4-dimethylamino-N-methyl-4-stilbazolium tosylate) crystal may also beused.

The detection unit 103 is a part for detecting the terahertz wavesthrough the probe light incoming from the laser unit 101. In thedetection unit 103, at the timing of incidence of the terahertz waves,the probe light is irradiated, and the resulting generated current isdetected. With this configuration, the terahertz waves are obtained. Forthe detection unit 103, the photoconductive element or the like havingthe antenna pattern on the semiconductor thin film similarly to thegeneration unit 102 is used.

The delay optical unit 104 is a part for optically adjusting the delayinterval of the probe light with respect to the pump light (the delaytime). While changing the delay time, the terahertz waves detected bythe detection unit 103 are measured, thus performing so-called terahertztime domain spectroscopy (THz-TDS). While changing the delay time, theresponse of the terahertz waves obtained from the detection unit 103 forevery delay interval is plotted by the processing unit 107, so that itis possible to obtain the time response of the terahertz waves. In FIG.1, for simplicity, illustrations of a chopper and the like necessary tothe THz-TDS are omitted. According to the present embodiment, asillustrated in FIG. 1, a reflection type optical system is provided tothe sample 109.

According to the present embodiment, it is characteristic that the delaytime adjustment unit 105 and the information storage unit 106 arefurther provided to this THz-TDS.

The information storage unit 106 is a part for pre-storing the internalinformation of the sample 109 as the standard information. For example,the position of the refractive index boundary face related to theinternal part of the sample 109 and the response waveform of theterahertz wave are stored. The information stored therein is obtainedfrom a specification at the time of manufacturing the sample 109. Also,the sample which becomes the standard and the time response waveform ofthe sample arbitrarily selected from among the sample group are measuredin advance (this measurement(s) may also be referred to herein as“previous measurement”), and this measurement result may be set as thestandard information. For example, the position of the refractive indexboundary face is found from the reflected waveform of this temporalresponse waveform to obtain the physical properties.

The delay time adjustment unit 105 is a part for controlling the delayoptical unit 104. Herein, reference is made to the standard informationon the internal part of the sample stored in the information storageunit 106, and in order to detect the terahertz waves from apredetermined measurement area in the depth direction such as therefractive index boundary face, the delay time of the probe light isadjusted. In a case where the measurement area to be desired to bedetected exists in a discontinuous manner, the delay time of the probelight is changed in a discontinuous manner. Then, by continuouslychanging the delay time only in the measurement area existing in adiscontinuous manner, the terahertz waves related to the measurementarea are detected. That is, a time when the terahertz waves reach thedetection unit 103 is predicted on a basis of the known internalinformation for the sample, and an adjustment is carried out on thedelay time of the probe light for operating the detection unit 103.

In this manner, the signal of the terahertz waves obtained from thedetection unit 103 partially loses a concept of the time axis as thedelay optical unit 104 is changed in a discontinuous manner (FIG. 2, thesignal of the detection unit). For example, as illustrated in FIG. 2,the delay time of the delay optical unit 104 is selected by the delaytime adjustment unit in a discontinuous manner like t1→t2→t3→t4, andresponses (1), (2), (3), and (4) of the terahertz waves in therespective delay times are obtained. For that reason, time informationbetween the measurement areas is missing. According to the presentembodiment, in order to compensate for this missing part, the processingunit 107 is used. For example, in the processing unit 107, a referenceis made to the adjustment amount of the delay time carried out by thedelay time adjustment unit 105, and the response of the terahertz wavesobtained by the detection unit 103 is reconstructed into the actual timeresponse of the terahertz waves (FIG. 2, the operation of the processingunit). To more be specific, time intervals of the responses (1), (2),(3), and (4) of the terahertz waves in the respective delay times areadjusted, and the response of the terahertz waves corresponding to theinternal information on the sample is obtained.

The operation of the terahertz wave apparatus will be described. In FIG.1, the terahertz wave pulse generated from the generation unit 102 isirradiated to the sample 109. The structure of the sample 109 at thistime is supposed to be the structure in FIG. 2. It is noted that for thesake of the operation description, herein, the structure of the sample109 is described while supposing that the thickness of a coating film202 is set as 300 μm (d1 and d3), and the thickness of a fine particle201 is set as 3 mm (d2). Also, for the simplification of the operationdescription, the refractive index of the respective materials issupposed to be 1, and the wavelength shortening effect due to therefractive index of these materials (the propagation length) thus neednot be taken into account. The terahertz waves incident on the sample109 are reflected, for example, by the refractive index boundary faceexisting in the sample 109. In the sample 109 of FIG. 2, the terahertzwaves are reflected by the surface of the coating film 202 structuringthe sample 109, the coating film 202, and the refractive index boundaryface of the fine particle 201. These reflected waves are incident on thedetection unit 103 with a time difference in accordance with thereflected position of the terahertz waves. In FIG. 1, a reflected pulsefrom the surface of the coating film 202 is denoted as (1), and areflected pulse from a boundary face between the coating film 202 andthe fine particle 201 is denoted as (2). Herein, for simplifying thedescription, a reflected pulse (3) from a boundary face between thecoating film 202 and the fine particle 201 and a reflected pulse (4)from a boundary face between the coating film 202 and the outside areomitted. As described above, when it is supposed that the film thicknessof the coating film 202 is set as 300 μm, the time difference betweenthe reflected pulses (1) and (2) is about 2 picoseconds (psec).

In the information storage unit 106, the information related to theinternal part of the sample 109 is pre-stored as the standardinformation. As described above, this standard information is obtainedfrom a specification at the time of manufacturing the sample or aprevious measurement of an arbitrarily selected sample. For example,positions on the time axis where the reflected pulse (1) and thereflected pulse (2) are generated, and the intensity, the pulse width,and the like of the respective reflected pulses are stored. For example,in a case where the positions on the time axis where the reflectedpulses are generated are stored in the information storage unit 106, thefollowing setting is established. It is noted that the position of thereflected pulse (1) varies depending on the measurement system of theapparatus, but herein, 5 psec is supposed.

The reflected pulse (1) . . . t1=5 psec

The reflected pulse (2) . . . t2=7 psec

The reflected pulse (3) . . . t3=27 psec

The reflected pulse (4) . . . t4=29 psec

Then, the positions on the time axis for the respective pulses are usedas the measurement reference for deciding the delay time of the delaytime adjustment unit 105. Also, as will be described later, in a casewhere the present apparatus is used for the screening of the sample 109these pieces of the standard information may also be used as informationfor the comparison.

According to the THz-TDS in the related art, the response waveforms fromthe reflected pulse (1) to the reflected pulse (4) are continuouslyobtained. However, according to the present embodiment, the delay timeadjustment unit 105 makes a reference to the time interval between thereflected pulses (1) and (2) stored in the information storage unit 106as the standard information to control the delay optical unit 104. Forexample, in the case where the time interval between the reflectedpulses (1) and (2) is 2 psec, the delay optical unit 104 adjusts theoptical length by 0.6 mm. Similarly, in the case of the time intervalbetween the reflected pulses (2) and (3), the delay optical unit 104adjusts the optical length by 6.0 mm, and in the case of the timeinterval between the reflected pulses (3) and (4), the delay opticalunit 104 adjusts the optical length by 0.6 mm.

For example, first, the delay time adjustment unit 105 refers to themeasurement reference obtained from the standard information which isstored in the information storage unit 106, to obtain the delay timegenerated by the reflected pulse (1). In this example, the delay timeadjustment unit 105 obtains 5 psec from the information storage unit 106as the delay time of the reflected pulse (1). Then, the delay timeadjustment unit 105 changes the distance through which the probe lightpasses in reaching the detection unit 103, by moving the delay opticalunit 104, and a desired delay time is provided to the apparatus. At thismeasurement position, in order to measure the reflected pulse (1), thedelay optical unit 104 continuously changes the delay time of the probelight. For example, in a case where a waveform having the pulse width of1 psec is desired to be obtained, the delay optical unit 104 is moved byabout 0.3 mm. It is noted that the term “continuously” herein means thatthe delay optical unit 104 is moved by a target distance in apredetermined interval. For example, when the predetermined interval isset as 100 μm, the delay optical unit 104 is moved at a constant speeduntil the delay optical unit 104 has been moved by 0.3 mm. Theprocessing unit 107 plots the signal of the detection unit 103 withrespect to the delay time which continuously changes, and the responsewaveform equivalent to the reflected pulse (1) is obtained.

After that, the delay time adjustment unit 105 refers to the measurementreference obtained from the standard information which is stored in theinformation storage unit 106, and obtains the delay time generated bythe reflected pulse (2). Herein, the delay time adjustment unit 105obtains 7 psec from the information storage unit 106 as the delay timeof the reflected pulse (2). Then, the delay time adjustment unit 105moves the delay optical unit 104 by 0.6 mm so as to obtain the delaytime when the reflected pulse (2) is generated again, and themeasurement operation of the reflected pulse (2) is started.

In this manner, the present embodiment includes a step of adjusting thedelay optical unit 104 by the delay time adjustment unit 105 in adiscontinuous manner. The response waveform of the terahertz wavesobtained in the processing unit 107 has a temporal waveform where thereflected pulses (1) and (2) continuously appear as illustrated in FIG.15A. As described above, this response waveform misses information onthe pulse interval between the respective pulses. For that reason, asillustrated in FIG. 15B, the processing unit 107 refers to themeasurement reference of the delay time carried out by the delay timeadjustment unit 105 in a discontinuous manner, and provides the timedifference of the respective measurement references to the reflectedpulse (1) and the reflected pulse (2), thus reconstructing the responsewaveform. Herein, a time interval 2 psec corresponding to the movementamount of the delay optical unit 104 is provided between the reflectedpulse (1) and the reflected pulse (2).

In this manner, according to the present embodiment, the method ofspecifying the rough measurement position by the information storageunit 106 and obtaining the response of the terahertz waves only in thepredetermined measurement position is used. With this configuration, itis not necessary to measure the terahertz waves continuously over theentire measurement time as in the THz-TDS carried out in the relatedart, and it is thus easier to shorten the measurement time for the timedifference between the respective measurement references.

FIG. 2 is a cross-sectional view and an operation of the sample 109 whena tablet is taken as being the sample 109. As illustrated in FIG. 2, thesample 109 has a form of consolidated fine particles 201 coated with acoating film 202. The fine particles 201 are obtained by consolidating apowdered state medicinal agent mixed with an additive. The coating film202 includes, for example, saccharose, a water-soluble polymer, aninsoluble polymer, etc. Depending on cases, a form without the coatingfilm 202 (uncoated tablet) is also conceivable. According to the presentembodiment, a sugar-coated tablet which is obtained by coating a coretablet with sugar is supposed. At this time, thicknesses d1 and d3 ofthe coating film 202 are often set as several tens of μm to severalhundreds of μm, and a thickness d2 of the tablet 109 is often set asseveral mm. As illustrated in FIG. 2, the terahertz waves irradiated onthe sample 109 become the reflected pulse (1) which is reflected by thesurface of the coating film 202. Also, the terahertz waves are reflectedby the refractive index boundary face such as the reflected pulses (2)and (3) which are reflected by the boundary face between the coatingfilm 202 and the fine particles 201, and then the reflected pulse (4)reflected again by the surface of the coating film 202. In general, inthe measurement based on short wavelengths such as visible light orX-rays, it is difficult clearly to distinguish this refractive indexboundary face. This is because, in general, the medicinal agent graindiameter is several tens of μm, and the shape of the boundary face ischanged in a complex manner while following the grain diameterdistribution of the fine particles 201 on the refractive index boundaryface. However, the value of the grain diameter is equivalent orsufficiently small as compared with the wavelength of the terahertzwaves. In other words, the wavelength of the terahertz waves ismoderately large, and the shape of the boundary face is not so clearlydetected as compared with the measurement of the short wavelength. Inother words, the unclear shape of the boundary face for shortwavelengths can be recognized as a relatively clear shape of theboundary face for terahertz waves. Also, the terahertz waves have amoderate transmissivity for the fine particles 201, and thus theterahertz waves are more suitable to obtain information on the boundaryface of the fine particles, as compared with a measurement based onshort-wavelength radiation like those mentioned above.

According to the present embodiment, these pieces of information on theboundary face are stored in the information storage unit 106, and in thedelay time adjustment unit 105, the positions (1), (2), (3), and (4) areselected and subsequently measured. For example, in a case whereregarding the respective pulses, a waveform of 2 psec converted on thetime axis is to be obtained, a measurement time of total 8 psec isnecessary. It is noted that as illustrated in FIG. 2, as the informationon the boundary face is sequentially measured, the response detected bythe detection unit 103 does not accurately reflect the information onthe thickness. According to the present embodiment, the processing unit107 converts the adjustment amount of the delay time of the probe lightadjusted by the delay time adjustment unit 105 to be reflected on theresponse waveform. As a result, it is possible to measure accurate filmthicknesses (d1′, d2′, and d3′).

In a case where the above-described operation is carried out through theTHz-TDS in the related art, the measurement time of about severalhundreds of psec is necessary. In contrast to this, in the configurationaccording to the present embodiment, it is possible to obtain theinternal information on the sugar coated tablet (sample) in ameasurement time of several psec as such a configuration is used thatthe rough measurement position is specified and only the waveformresponse at the measurement position is obtained to carry out thereconstruction. For that reason, as compared with the method in therelated art, the measurement at a higher speed is facilitated.

It is noted that according to the present embodiment, the film thicknessin the depth direction of the sample 109 has been described, but thepresent invention is not limited to the above. As illustrated in theTHz-TDS in the related art, by using the intensity and the delayinformation on the terahertz waves at the selected measurement position,it is also possible to measure the change of the physical properties,the difference of the crystal structures, the blend ratio, thecomposition, the density of the fine particles, a material having adesired physicality, and the like. For example, as a method of obtainingthe physical properties, the complex refractive index is obtained fromthe intensity of the reflection pulse and the delay time, and thedesired physical property is converted therefrom. It is also possible toadopt a mode of measuring this change of the physical property.Moreover, by verifying the difference of the fingerprint spectra in theterahertz region, it is also possible to determine a difference incrystal structures. Furthermore, the fingerprint spectrum obtained issupposed to be composed of the fingerprint spectrum related to aplurality of substances, and it is also possible to predict the blendratio from a computation for separating the spectra or the intensity orspread of the respective spectra. Alternatively, such a mode may also beadopted that the determination is carried out while the analytical curveof the respective spectra which follow the thickness or concentration ofthe sample is used. On the basis of the transmissivity, thereflectivity, or the spectrum information related to these, the densityof the fine particles can also be verified. In a similar manner, theverification of the composition for finding out which molecules anaggregation of the substance is made of can also be carried out. Thesemethods are appropriately combined and selected while followingpurposes.

It is noted that according to the present embodiment, the tablet isexemplified as the sample 109, but the present invention is not limitedto the above. Generally, it should be considered that any sample withwhich internal information of a material can be efficiently obtained maybe used.

Second Embodiment Transmission Type

The present embodiment illustrates a mode related to the terahertz wavedetection apparatus according to the present embodiment. To more bespecific, the present embodiment illustrates a modified example of theterahertz wave detection apparatus according to the first embodiment. Itis noted that that part of the description which is common to thisembodiment and the above-described embodiment will be omitted.

FIG. 3 illustrates a modified example of the terahertz wave detectionapparatus according to the present embodiment. As illustrated in FIG. 3,in the terahertz wave detection apparatus according to the presentembodiment, the propagation path of the terahertz waves has atransmission type optical arrangement with respect to the sample 109.

The operation of the terahertz wave detection apparatus according to thepresent embodiment will be described. It is noted that in thedescription of the operation, a description on a common part will beomitted. Herein, the sample 109 is supposed to be the same as that ofthe first embodiment. That is, for the structure of the sample 109, itis supposed that the thickness of the coating film 202 is 300 μm, andthe thickness of the fine particle 201 is 3 mm. Also, the refractiveindex of the respective materials is supposed to be 1 for simplifyingthe operation description, and the wavelength shortening effect due tothe refractive index of these materials (the propagation length) is nottaken into account. Herein, the transmitted pulse detected by thedetection unit 103 is supposed to be the transmitted pulse illustratedin FIG. 16. As illustrated in FIG. 16, a transmitted pulse (1) is apulse transmitted through the sample 109. A transmitted pulse (2) andthe transmitted pulse (3) are pulses reflected by the surface of thecoating film 202 and reflected by the boundary face between the coatingfilm 202 and the fine particle 201 once. A transmitted pulse (4) is apulse reflected between the surfaces of the coating film 202 once.

For example, the information storage unit 106 stores positions on thetime axis where these transmitted pulses are generated. It is noted thatpulses other than the above-described transmitted pulses also exist. Forexample, such pulses include a transmitted pulse reflected by theboundary face twice or a transmitted pulse reflected by a boundary facedifferent from the above-described boundary face, etc. The detectionunit 103 detects, in addition to the transmitted pulse necessary to theinspection, these pulses mixed on the time axis in enumeration.According to the present embodiment, the positions on the time axispre-stored in the information storage unit 106 are limited, and it isthus possible to carry out the inspection while filtering the pulseswhich are not used for the inspection. Therefore, inspection efficiencyis increased.

According to the present embodiment, the positions on the time axis ofthe transmitted pulse are set as follows. It is noted that the positionof the transmitted pulse (1) changes due to the setting of themeasurement system of the apparatus, but herein, 5 psec is supposed.

The transmitted pulse (1) . . . t1=5 psec

The transmitted pulse (2) . . . t2=7 psec

The transmitted pulse (3) . . . t3=27 psec

The transmitted pulse (4) . . . t4=29 psec

The position of the respective transmitted pulse on the time axis areused as the measurement reference for deciding the delay time of thedelay time adjustment unit 105. The adjustment amounts of the delayoptical unit 104 with respect to these delay times are as follows.

From the transmitted pulse (1) to the transmitted pulse (2) . . . 0.6 mm

From the transmitted pulse (2) to the transmitted pulse (3) . . . 6.0 mm

From the transmitted pulse (3) to the transmitted pulse (4) . . . 0.6 mm

By adopting such an optical arrangement, the terahertz waves have a modeto be transmitted through the internal part of the sample 109. For thatreason, the terahertz waves propagating through the sample 109 have aresponse which reflects the rough characteristic features in the depthdirection of the sample 109. For example, when the medicinal agentillustrated in FIG. 2 is supposed as the sample 109, from the absorbanceindex the first transmitted pulse (1), it is possible to estimate thedensity of the entire sample 109, the absorbed amount of the terahertzwave, the composition, and the like. Also, by monitoring the phase shiftamount (or the time delay amount), the thickness of the entire sample109 can be estimated.

In this manner, by adopting the transmission type arrangement, it ispossible to easily estimate the overall characteristic features of theobject to be measured.

Third Embodiment Comparison Unit

FIG. 4 illustrates a mode related to an inspection system according tothe present invention. As illustrated in FIG. 4, the inspection systemaccording to the present embodiment has a configuration in which acomparison unit 410 and an apparatus control unit 411 are added to theconfiguration of the terahertz wave detection apparatus according to thefirst embodiment. Description of parts common to this embodiment and tothe first embodiment will be omitted.

The comparison unit 410 refers to the internal information of the sample109 obtained by the processing unit 107 and the internal informationwhich becomes the standard of the sample 109 previously stored in theinformation storage unit 106. Then, a difference between the signal ofthe processing unit 107 obtained through the actual measurement and theinformation in the information storage unit 106 is monitored todetermine whether the sample 109 in the desired state is obtained.

For example, in a case where the sugar-coated tablet is supposed as thesample 109, the information storage unit 106 stores the thickness of thesugar-coated tablet and the information on the boundary face between thecoating film and the tablet (the thickness, and the like). Thisinformation is obtained from the manufacturing condition for the sample109. Also, the sample 109 which becomes a reference is selected, and themeasurement data on the terahertz waves with respect to the sample 109may be used as the internal information which becomes the standard. Inthe comparison unit 410, a permissible range of an error is set withrespect to this information in the information storage unit 106. In acase where the comparison unit 410 carries out the monitoring on thecoating film thickness of the sample 109, the permissible error range ofthe coating film thickness is set in a range where a desired amount ofmedicinal properties reach a target affected area. It is noted thataccording to the present embodiment, this permissible error range is setby the comparison unit 410, but the setting position is not limited tothe above. For example, in the information storage unit 106, a mode ofproviding this permissible error range together with the information onthe sample 109 may also be adopted.

Also, according to the present embodiment, the information to becompared does not necessarily have to be the response waveform of theterahertz wave. For example, only the intensity of the terahertz wavesin the predetermined measurement area can be set as the comparisontarget too. Also, it is possible to adopt a mode of monitoring whetherthe intensity at the measurement position falls within the setpermissible error range. To more be specific, this mode is to measurethe signal intensity at the apex of the respective pulses in FIG. 2.From the change in the signal intensity at the measurement position, thetemporal position of the response waveform of the terahertz waves isestimated. In this manner, a mode for setting only the intensity at themeasurement position as the measurement and inspection target can alsobe applied to the above-described embodiments.

As illustrated in FIG. 4, according to the present embodiment, theplurality of samples 109 are provided, and the respective samples aresequentially conveyed by the conveyance unit 108. In the comparison unit410, with respective to the samples 109, the measurement data of thesample 109 obtained by the processing unit 107 is compared with theinformation in the information storage unit 106 which becomes thestandard to monitor whether the measurement data falls within thepermissible error range. Then, the comparison unit 410 determines thesample 109 indicating a characteristic feature out of this permissibleerror range as a defective product. The apparatus control unit 411 is apart for controlling the apparatus in response to the comparison resultof the comparison unit 410. For example, in the case of screening thesamples 109 conveyed by the conveyance unit 108, the control is carriedout so as to remove the sample 109 identified as a defective product.The sample 109 to be removed may be only the sample 109 that has beenidentified as itself being defective, or may be a group neighboring andincluding the sample 109 that is defective. Also, in response to theresult of the comparison unit 410, the apparatus control unit 411 mayadopt a mode of feeding the manufacturing condition in the manufacturingstep for the sample 109 back to a desired condition. For example, in acase where the sugar-coated tablet is supposed as the sample 109, thefilm thickness of the coating film is adjusted. Also, in a case wherethe physical property of the boundary face between the coating film andthe tablet exceeds the permissible error as the blend ratio of themedicinal agent to the additive agent changes or the crystal structureof the medicinal agent changes, for example, the adjustment on thesemanufacturing conditions are carried out.

With such a configuration, it is possible to inspect the inside of theobject to be measured in a nondestructive manner. Also, similarly to thefirst embodiment, such a mode is adopted that reference is made to theinformation about the inside of the sample which serves as thereference, and the measurement range is limited. Then, the response ofthe terahertz waves is reconstructed, so that high speed measurement isfacilitated. In particular, the mode is preferably used for theinspection system for the medicinal agent.

Also, according to the present embodiment, the inspection part due tothe terahertz waves has the reflection type configuration, but theconfiguration is not limited to the above. For example, the inspectionpart due to the terahertz waves may have the transmission typeconfiguration illustrated in the second embodiment. In thisconfiguration, as described above, it is possible in a simple way toestimate the overall characteristic features of the sample. For thatreason, for example, it is also possible to add a first-stage screeningfunction of checking the mixture of a foreign substance or the presenceor absence of a crack on the basis of the absorbed amount of theterahertz waves or the phase shift. After that, the internal inspectionmay be carried out only on the samples in which it is checked that thereare no macro-structural defects, and therefore it is possible to carryout the inspection effectively.

Fourth Embodiment A Plurality of Delay Optical Units

The present embodiment illustrates a modification example related to theabove-described terahertz wave detection apparatus. To be specific, themodification example relates to an optical system for obtaining theterahertz waves. It is noted that a part of the description that iscommon to the above-described embodiment will be omitted.

FIG. 5 relates to the above-described apparatus, illustrating anothermode of the delay optical unit 104. As illustrated in FIG. 5, the delayoptical unit 104 according to the present embodiment is composed of aplurality of delay optical units 504 a and 504 b. Then, the respectivedelay optical units are respectively adjusted to the measurementpositions selected by the delay time adjustment unit 105.

For example, as described in the above-described embodiment, such a caseis considered that the terahertz waves propagating from the sample 109have pulses (1) and (2). According to the above-described embodiments,the delay time adjustment unit 105 is used to sequentially move thedelay optical unit 104 to the positions corresponding to the respectivepulses. According to the present embodiment, as illustrated in FIG. 5,the delay optical unit 504 a and the delay optical unit 504 b arerespectively allocated to the position corresponding to the reflectionpulse (1) and the position corresponding to the reflection pulse (2) tomeasure the response of the terahertz waves.

Herein, the two delay optical units may suffice if the set opticallength is ensured, and the positional relation between the two delayoptical units is not particularly limited.

It is noted that according to the present embodiment, the respectivedelay optical units respectively correspond to the respective reflectionpulses of the terahertz waves propagating from the sample 109, but themode is not limited to the above. For example, such a mode may also beadopted that the pulses of the terahertz waves are set as a plurality ofreflection pulse groups, and the delay optical units are respectivelyallocated to the respective reflection pulse groups. In this case, thedelay time adjustment unit 105 carries out the operation of setting themeasurement positions with respect to the respective reflection pulsegroups and sequentially moving the allocated delay optical units.

In this manner, by using the plurality of delay optical units to beoperated in parallel, it is possible to shorten the period of timeneeded for measuring the response of the terahertz waves. For thatreason, it is possible to operate the apparatus according to theembodiment of the present invention at a still higher speed. Also, asillustrated in FIG. 10 it is also possible to such a configuration thatthe plurality of detection units are allocated to the respective delayoptical units. In this case, as compared with the mode of processingthrough the single detection unit, the standby time for measuring therespective reflection pulses is shortened, and higher-speed operation ofthe apparatus is facilitated.

Fifth Embodiment Plurality of Detection Units

The present embodiment illustrates a modified example related to theabove-described terahertz wave detection apparatus. To be specific, themodified example relates to the arrangement of the detection unit 103.It is noted that a part of the description common to the above-describedembodiment will be omitted.

FIG. 9 relates to the apparatus described thus far, illustrating anothermode of the detection unit 103. As illustrated in FIG. 9, the pluralityof detection units 103 according to the present embodiment are provided.

For example, such a case is supposed that depending on a state of theinternal part of the sample 109, the propagating directions of therespective pulses of the terahertz wave for propagating the sample 109are different. To be specific, the propagating directions of the pulses(1) and (2) of the terahertz wave are different from each other. In acase where the plurality of refractive index boundary faces of thesample 109 have different angles with respect to the incidence directionof the terahertz waves, the propagating directions of the pulses (1) and(2) of the terahertz waves are different from each other. For thedetection unit 103, an arrangement in which it is possible to obtain theterahertz waves at the highest sensitivity is a configuration ofarranging the detection unit 103 in the middle of the propagating pathof the terahertz waves. Herein, the arrangement providing thesatisfactory sensitivity refers to an arrangement in which the intensityof the terahertz waves detected by the detection unit 103 becomesstrongest. When the pulses having different propagating directionsexist, for example, a phenomenon may occur in which the sensitivity topulse (1) is satisfactory, but as to pulse (2), the intensity of theterahertz waves reaching the detection unit 103 becomes small, and thedetection sensitivity is decreased. For that reason, a plurality ofdetection units 903 a and 903 b are arranged at positions where it ispossible to obtain the terahertz waves at the highest sensitivity forthe respective pulses. According to the present embodiment, thedetection unit 903 a is allocated to the pulse (1), and the detectionunit 903 b is allocated to the pulse (2). Then, while corresponding tothe measurement position selected by the delay optical unit 104, by alight path switching unit 914, the probe lights (1) and (2) arerespectively allocated to the detection units 903 a and 903 b. Then, themeasurement and the inspection are carried out at the highestsensitivity for the respective pulses.

It is noted that as described in the fourth embodiment, according to thepresent embodiment, the pulses of the terahertz waves propagating fromthe sample 109 correspond to the respective detection units, but thepresent invention is not limited to this mode. For example, for thepulses of the terahertz waves, the pulses having substantially the samepropagating direction are set as one pulse group. At this time, thedetection units are allocated to the respective pulse groups.

With such a configuration, the detection unit can be optimized to thepropagating directions of the respective pulses, and therefore theimprovement in the detection sensitivity can be expected. Also, asillustrated in FIG. 10, instead of the light path switching unit 914,such a mode may be used that the plurality of delay optical unitsdescribed in the fourth embodiment are used. At this time, therespective delay optical units are allocated with pulses insubstantially the same propagating direction. In this case, as comparedwith the mode of processing the single delay optical unit 104, thestandby time to measure the respective pulses is decreased, and thus thehigher speed of the apparatus is facilitated.

Sixth Embodiment Accumulation Processing by Counting Measurement Times

The present embodiment illustrates a modified example related to theabove-described terahertz wave detection apparatus. To be specific, themodified example relates to a method of obtaining the terahertz wave. Itis noted that a part of the description common to the above-describedembodiment will be omitted.

As illustrated in FIG. 6, the apparatus according to the presentembodiment has a configuration of being further provided with a counterunit 612 for measuring the number of times to measure the response ofthe terahertz wave and record the number of times to carry out themeasurements. According to the present embodiment, the counter unit 612sets the number of times to carry out the measurements and counts thenumber of the samples 109 which are measured up to this number ofmeasurements. According to the configurations described thus far,regarding the sample 109 conveyed by the conveyance unit 108, onemeasurement is carried out on the one sample 109. If the plurality ofsamples 109 conveyed by the conveyance unit 108 are the same, themeasurement results obtained from the respective samples 109 aresubstantially the same. According to the present embodiment, theprocessing unit 107 carries out the accumulation processing on theplurality of measurement results by the number of measurement times tobe recorded in the counter unit 612, and the average measurement resultis obtained. In other words, herein, not the measurement result of theindividual sample 109, but the average measurement result for the groupof the plurality of samples 109 is obtained. The measurement mode may bea mode of continuously measuring the adjacent samples 109 or a mode ofdiscretely measuring the samples at a certain number interval.

It is noted that in FIG. 6, the processing unit 107 carries out theaccumulation processing on the basis of the number of the samples 109 tobe measured, but the present invention is not limited to this mode. Forexample, as illustrated in FIG. 7, such a configuration may also beadopted that a counter unit 712 configured to divide the measurementtime accumulates the data measured by the detection unit 103 in thepredetermined measurement time.

Also, according to the above-described embodiments, such a mode has beendescribed that the terahertz waves are sequentially irradiated to theindividual sample 109, but the present invention is not limited to thismode. For example, as illustrated in FIG. 8, such a configuration mayalso be adopted that by widening the irradiation area of the terahertzwaves, the plurality of samples 109 are collectively irradiated with theterahertz waves.

In this manner, by providing the configuration of accumulating theresponses from the plurality of objects to be measured, it is possibleto mitigate the influence of the noise depending on the measurementsystem or the measurement environment, and the improvement in the signaldetection accuracy is expected.

Seventh Embodiment Fiber Laser

The present embodiment illustrates a mode related to the terahertz wavedetection apparatus. To be specific, the present embodiment relates to amodification example of the laser unit 101. It is noted that a part ofthe description common to the above-described embodiment will beomitted.

According to the above-described embodiments, a titanium-sapphire laseris used for the laser unit 101, but according to the present embodiment,a fiber laser is used.

The fiber laser is a small and stable ultrashort pulse laser sourcewhich is, mainly, an optical laser. A configuration example of the fiberlaser is illustrated in FIG. 11. As illustrated in FIG. 11, the fiberlaser is realized by including the following components:

A femtosecond fiber laser 1101

½ wavelength plates 1102 and 1106

An amplification unit 1103

An isolator 1104

A dispersion compensation unit 1105

A polarizing beam splitter 1107

A PPLN (Periodically Poled Lithium Niobate) element 1108 which is anefficient wavelength conversion element

A green cut filter 1109

A dichroic mirror 1110

The femtosecond fiber laser 1101 uses the optical laser for anoscillation medium. The center wavelength is 1558 nm, the averageintensity is 5 mW, the pulse width is 300 fsec, and the cyclic frequencyis 48 MHz. The femtosecond fiber laser 1101 of this type is smaller andmore stable as compared with a solid-state laser. The ½ wavelengthplates 1102 and 1106 are used for adjusting the polarization. Theamplification unit 1103 is a part configured to amplify the intensity ofthe light pulse from the femtosecond fiber laser 1101. The light pulsewhose intensity is amplified by the amplification unit 1103 is convertedinto a short pulse by the dispersion compensation unit 1105. The PPLN1108 is a part configured to generate a component of 780 nm which is thesecond order harmonic component of the light pulse converted into theshort pulse. After that, by using the green cut filter 1109 and thedichroic mirror 1110, the harmonic component 780 nm as well as thereference wave component 1550 nm are output at a desired branchingratio. This harmonic component is equivalent to the absorbing wavelengthof LT-GaAs, and is used for the exciting light of the photoconductiveelement according to the present embodiment. It is noted that in a casewhere InGaAs is used for the semiconductor thin film used for thephotoconductive element, the reference wave component can also be usedfor the exciting light for exciting the carrier. In this case, theoptical system for generating and taking out the higher harmonic wavecan also be omitted.

Hereinafter, details related to the amplification unit 1103 and thedispersion compensation unit 1105 will be described.

FIG. 12 illustrates a configuration example of the amplification unit1103. As illustrated in FIG. 12, the amplification unit 1103 is realizedby including the following components:

Three laser diodes (which are referred to as LDs in the drawing)

A single mode fiber 1201

WDM (Wavelength Division Multiplexing) couplers 1202 and 1205

A polarization controller 1203

An Er (erbium) added fiber 1204

A polarization beam combiner 1206

With respect to the wavelength of 1.56 μm, the single mode fiber 1201has the second order group velocity dispersion of −21.4 ps²/km, the modefield radius of 9.3 μm, the nonlinear coefficient of 1.89 W⁻¹ km⁻¹, andthe fiber length of 4.5 m. With respect to the wavelength of 1.56 μm,the Er added fiber 1204 has the second order group velocity dispersionof 6.44 ps²/km, the mode field radius of 8.0 μm, the nonlinearcoefficient of 2.55 W⁻¹ km⁻¹, and the fiber length of 6.0 m. The threeLDs has the wavelength of 1480 nm and the intensity of 400 mW. Asillustrated in FIG. 12, one of the LDs is used for forward excitation,and two of the LDs are used for backward excitation.

The pulse width of the light pulse incoming from the femtosecond fiberlaser 1101 is expanded in the single mode fiber 1201 due to an influenceof group velocity dispersion. With this configuration, the peakintensity of the light pulse is temporarily suppressed. As a result, thelight pulse can suppress the excess nonlinear effect generated at thetime of the propagation in the Er added fiber 1204, and therefore it ispossible to carry out the effective energy amplification. According tothis configuration, the average intensity of the light pulses can beexpected to be about 20 dB.

FIG. 13 illustrates a configuration example of the dispersioncompensation unit 1105. The dispersion compensation unit 1105 has adispersion characteristic which is inverse to the dispersioncharacteristic generated by the amplification unit 1103. The light pulseoutput from the amplification unit 1103 has a tendency to have the bandwidely spread due to an influence of the self-phase modulation generatedin the Er added fiber 1204. In view of the above, in the dispersioncompensation unit 1105, the dispersion in the respective wavelengths iscompensated, so that a pulse shorter than the pulse width of thefemtosecond fiber laser 1101 is obtained. As illustrated in FIG. 13,according to the present embodiment, a dispersion compensation fiber1301 is used for the dispersion compensation unit 1105. To be specific,as the dispersion compensation fiber 1301, a large hole diameterphotonic crystal fiber is used. With respect to the wavelength of 1.56μm, the dispersion compensation fiber 1301 used in the presentembodiment has the second order group velocity dispersion of −30.3ps²/km, the mode field radius of 26 μm, the nonlinear coefficient of0.182 W⁻¹ km⁻¹, and the fiber length of 0.42 m. With this configuration,the obtained pulse width of the light pulse can be expected to be about55 fsec, and the average intensity can be expected to be about 280 mW.

As described above, for the semiconductor thin film of thephotoconductive element, in a case where LT-GaAs is used, the secondhigher harmonic wave is generated by the PPLN 1108 to obtain theexciting light. In the PPLN 1108, in addition to this harmonic component(780 nm), the reference wave component (1550 nm) is output, and thus,the dichroic mirror 1110 is used for separation. Also, in the PPLN 1108,in addition to the second higher harmonic wave, green light which is thethird higher harmonic wave is slightly generated, and thus the greenlight is removed by the green cut filter 1109. According to such aconfiguration, the pulse width of the light pulse in the 780 nm band canbe expected to be about 58 fsec, and the average intensity can beexpected to be about 60 mW. Also, the pulse width of the light pulse inthe 1550 nm band can be expected to be about 64 fsec, and the averageintensity can be expected to be about 170 mW.

In some cases, as illustrated in FIGS. 14A and 14B, it is also possibleto carry out the pulse compression by using the highly-nonlinear fiber.FIG. 14A is a structural drawing for compressing the light pulse in the1550 nm band. Also, FIG. 14B is a structural drawing for compressing thelight pulse in the 780 nm band. It is noted that these configurationsare merely an example mode, and the method of carrying out the pulsecompression is not limited to this method.

In FIG. 14A, in order to carry out the pulse compression in the 1550 nmband, a single mode fiber 1401 and a highly-nonlinear fiber 1402 areused. With respect to the wavelength 1.56 μm, the single mode fiber 1401has the second order group velocity dispersion of −21.4 ps²/km, thenonlinear coefficient of 1.89 W⁻¹ km⁻¹, and the fiber length of 0.115 m.With respect to the wavelength 1.56 μm, the highly-nonlinear fiber 1402has the second order group velocity dispersion of −14.6 ps²/km, thenonlinear coefficient of 4.53 W⁻¹ km⁻¹, and the fiber length of 0.04 m.Also, the light pulse output from the fiber has a parabolic mirror tocollimate so as to avoid the pulse spread due to the dispersion in thelens. According to such a configuration, the obtained pulse width of thelight pulse can be expected to be about 22 fsec, and the averageintensity can be expected to be about 120 mW.

In FIG. 14B, in order to carry out the pulse compression in the 780 nmband, the highly-nonlinear fiber 1402 and a chirped mirror 1403 areused. The chirped mirror 1403 is a negative dispersion chirped mirror.Each time the mirror has one reflection, a dispersion of about −35 fs²is applied. While the light pulse is reflected between the chirpedmirrors 1403 by plural times, the pulse compression is carried out.Herein, 1 m of the highly-nonlinear fiber 1402 is used. According tosuch a configuration, the obtained pulse width of the light pulse can beexpected to be about 37 fsec, and the average intensity can be expectedto be about 30 mW. According to the present embodiment, this light pulseis used as the exciting light of the photoconductive element. It isnoted that the specific configuration and the respective parameters ofthe fiber laser are not limited to the above, and can be appropriatelyselected in accordance with various purposes by one of ordinary skill.

Also, according to the present embodiment, the photoconductive elementis used for the generation unit 102. As described above, by using thesemiconductor substrate having no electrodes or the organic crystal, itis possible to suppress the limitation of the terahertz wave band due tothe electrode configuration, and the response waveform of a still widerband (the narrow pulse width) can be expected. To be specific, DASTcrystal (4-dimethylamino-N-methyl-4-stilbazolium tosylate) is used forthe generation unit 102, and the photoconductive element based onLT-gaas is used for the detection unit 103. At this time, from the fiberlaser, by irradiating the light in the 1550 nm band as the probe lightand the light in the 780 nm as the probe light, it is possible togenerate the terahertz wave having the half bandwidth of about 200 fs(the band to about 7.5 THz).

In this manner, by using the fiber laser for the laser unit 101,stability, a smaller size, and a lower price for the apparatus can beexpected.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures and functions.

This application claims the benefit of Japanese Application No.2007-226338 filed Aug. 31, 2007 and No. 2008-159315 filed Jun. 18, 2008,which are hereby incorporated by reference herein in their entirety.

1. An apparatus for obtaining information related to terahertz waves transmitted through or reflected by a sample, the apparatus comprising: a generation unit arranged to generate terahertz waves; a detection unit arranged to detect terahertz waves which are generated by the generation unit and transmitted through or reflected by a sample; a delay unit arranged to change a timing for the detection unit to detect the terahertz waves; a storage unit arranged to pre-store information related to internal information of the sample as a standard information; a waveform obtaining unit arranged to obtain a temporal waveform of the transmitted or reflected terahertz waves which are obtained by the delay unit; and a delay time adjustment unit arranged to control the delay unit on the basis of the standard information pre-stored in the storage unit, wherein the terahertz waves from the sample include a first pulse and a second pulse, wherein the delay time adjustment unit adjusts the delay unit in a discontinuous manner on the basis of a position on a time axis for the first pulse and the second pulse, and wherein the waveform obtaining unit reconstructs the temporal waveforms by providing a time interval between the first pulse and the second pulse.
 2. The apparatus according to claim 1, wherein the information related to the sample pre-stored in the storage unit is a temporal waveform of the terahertz waves transmitted through or reflected by the sample, which is previously obtained by the waveform obtaining unit.
 3. The apparatus according to claim 1, wherein the area is a pulse of the temporal waveform.
 4. The apparatus according to claim 1, wherein the waveform obtaining unit obtains a temporal waveform of the terahertz waves transmitted through or reflected by the sample by sampling the terahertz waves detected by the detection unit on the basis of the timing changed by the delay unit.
 5. The apparatus according to claim 1, wherein the delay unit changes at least one of the timing for generating the terahertz waves and the timing for detecting the terahertz waves.
 6. The apparatus according to claim 1, wherein the information related to the sample is obtained on the basis of the temporal waveform of the transmitted or reflected terahertz waves in the area.
 7. The apparatus according to claim 1, wherein the temporal waveform of the transmitted or reflected terahertz waves in the area is compared with the information pre-stored in the storage unit to derive a state of the sample.
 8. The apparatus according to claim 1, further comprising a fiber laser configured to generate pulse laser light, wherein the fiber laser comprises: an optical fiber used as an oscillation medium of the pulse laser light; an amplification unit arranged to amplify an intensity of an optical pulse oscillated from the optical fiber; and a dispersion compensation unit arranged to reduce a width of the amplified optical pulse, wherein the generation unit comprises a photoconductive element configured to generate the terahertz waves through irradiation of the pulse laser light, and wherein the detection unit comprises a photoconductive element configured to detect the terahertz waves through the irradiation of the pulse laser light.
 9. The apparatus according to claim 1, wherein the apparatus comprises a plurality of the detection units, the plurality of the detection units being arranged corresponding to propagating directions of the terahertz waves transmitted through or reflected by the sample; and wherein the apparatus further comprises a light path switching unit for propagating the terahertz waves to one of the plurality of detection units arranged corresponding to the propagation directions.
 10. The apparatus according to claim 1, wherein the apparatus comprises a plurality of the detection units, the plurality of the detection units being arranged corresponding to propagating directions of the terahertz waves transmitted through or reflected by the sample; and wherein the apparatus further comprises a light path switching unit for propagating the terahertz waves to one of the plurality of detection units arranged corresponding to the propagation directions.
 11. A method for obtaining information related to terahertz waves transmitted through or reflected by a sample, the method comprising the steps of: generating terahertz waves; detecting a first pulse of the terahertz waves that is transmitted through or reflected by a sample; obtaining a movement amount of a delay unit by using information related to the sample; moving the delay unit by the obtained movement amount; detecting a second pulse of the terahertz waves that is transmitted through or reflected by the sample; obtaining a state of the sample from the first pulse and the second pulse; and outputting or storing the state of the sample as an inspection result, wherein the sample comprises a plurality of reflection interfaces, wherein the information related to the sample is a distance between the reflection interfaces, wherein the moving amount of the delay unit is obtained by using the distance, wherein a state of the reflection interface is obtained from the first pulse and the second pulse, wherein a permissible error range of the distance is set, and wherein the sample indicating a characteristic feature out of the permissible error range is determined as a defective product. 